What are the important reasons for the inconsistency of lithium batteries?

First, there are subtle differences in processing techniques and materials. Under long-term use, the material aging speed of each battery is not synchronized, which will cause large differences in the voltage, internal resistance, and capacity of a single battery. Second, different processing batches. Due to different initial conditions and losses, putting them in the same battery pack will cause imbalance, and as time goes by, the imbalance will increase. Third, some minor defects during the processing of some batteries may cause these batteries to have a resistance leakage path of more than 40k, forming a soft short circuit phenomenon. And this soft short circuit is one of the important reasons that cause some batteries to be unbalanced. Fourth, the performance of the batteries of the same batch is usually very similar, but due to the large temperature change of the battery pack, some of the batteries are heated more, which makes their own losses increase, which causes imbalance. In severe cases, hot spots may appear in the battery pack, and such an imbalance is very dangerous. Fifth, in the battery pack, due to the different positions of the single cells in the series, different system leakage will occur on the battery protection board. The leakage power may be small, but it will also cause battery imbalance for a long time. Battery imbalance threatens safety. These imbalance phenomena not only reduce the capacity of the battery pack, but may even cause serious safety hazards such as overcharge and overdischarge. Let us conduct a careful analysis of these two situations: first, the case where the capacity of the battery pack becomes smaller;. Take the application of a three-string battery pack as an example. Initially, the three single cells of A, B, and C have 100% capacity. However, under long-term use, the batteries appear unbalanced, causing at a certain moment, A battery Remaining 80% capacity, B battery remaining 40% capacity, C battery remaining 60% capacity; at this time, the battery pack is charged. Due to the over-voltage protection purpose, when A battery is 100% full and the charger is turned off, B battery The capacity is only 60%, and the capacity of the C battery is 80%, so that the B battery and C battery in the battery pack are not fully charged. When discharging the battery pack, due to the purpose of under-voltage protection, when the B battery is discharged to 0% (ideal value), the A battery will still have 40% capacity, and the C battery will still have 20% capacity. The battery A and C in the battery pack are not fully discharged. (The change in charge/discharge capacity after the three strings of batteries are out of balance is shown in Table 1). Secondly, for situations that may cause severe overcharge and overdischarge. Take a 4-string battery pack as an example (single cell overvoltage point is 4.2V; undervoltage point is 3.0V; only the total voltage of the battery pack is protected, without single cell voltage monitoring. As shown in Figure 1), it is used for a long time Next, the battery appears unbalanced. Without single battery voltage monitoring, while discharging, although the battery pack meets the 12V under-voltage protection setting, it is composed of 3.6V+3.2V+3.2V+2.0Vu003d12V, of which the lowest imbalance The battery voltage has dropped to 2.0V and a serious overdischarge has occurred. When charging, although the overvoltage protection setting of 16.8V is met, it is composed of 4.7V+4.1V+4.1V+3.9Vu003d16.8V, and the highest unbalanced battery voltage has reached 4.7V, which is a very dangerous overcharge phenomenon. The resistance equalization method has great potential. After knowing the reasons and shortcomings of the battery imbalance, we should consider the appropriate equalization current when designing the battery equalization method, consider the timing of the equalization function, consider the accuracy of the battery balance, and consider the combination of multiple batteries. Carry out the balance and consider the heat dissipation problem in the overall balanced design. Nowadays, how to economically and reliably solve the problem of monomer imbalance in multi-cell battery packs is becoming more and more important for the promotion of applications such as electric tools, electric bicycles, and light electric vehicles. There are many methods of equilibrium in theory, and among them, the resistance (shunt) equilibrium method is considered to be the most economical and practical one at present. On this basis, OMicro has proposed the latest intelligent balancing technology, Battery Bleeding-on-Demand (BOD) technology. The settings of each equalization parameter provided by this technology are part of the overall heat dissipation consideration when designing battery equalization. For applications with high equilibrium heat loss restrictions, you can choose low equalization current, higher equalization starting voltage, lower equalization accuracy, and fewer simultaneous equalization batteries to reduce equalization heat loss; and when the battery pack has ample thermal capacity , You can choose higher equalization current, lower equalization starting voltage, higher equalization accuracy, and more simultaneous equalization batteries to improve the equalization speed. Disclaimer: The articles published on this website are all from the Internet. If there is any infringement, please contact to delete it. Disclaimer: Some pictures and content of the articles published on this site are from the Internet. If there is any infringement, please contact to delete. 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